How safe is it nowadays to backpack through Europe alone?
As an european resident (Netherlands), I can say that travel in Europe is safe. Of course, you need to take the same precautions as you would when backpacking the US. Avoid certain areas/parts of big cities, try to combine your travels with fellow travellers, don’t stay out at night, but other than that, you should definitely be fine. Especially Western Europe (UK, Netherlands, France, Spain, Italy, Germany) is perfectly safe. You might want to avoid going too much eastern though.